Highly dislike the desynth system

[HEC]

You can only cap 2, each class starts at 1 and is subtracted from the 300 total.

Yes and no ... of course if you have all DoH at 30+ (usually 50) then you're missing 5 points in total so in theory you can reach only 295 on three you've decided to level up desynth on. If the other classes will be unable to drop bellow 1 you're indeed stuck at 295. However if you'd have only 3 DoH classes at 30+ and all other bellow 30 (loosing thus many crossclass abilities) you can in theory reach 300 so most logical solution would be to level up 2 most usefull desynths on your main and then other 3 (plus another 3 if you feel like) on your alt(s) while keeping any other "unwanted" classes bellow 30 there (or not level them at all if you don't care about crossclass skills, after all you can craft anything you need for leveling on your main anyway). Indeed there is an issue with passing items and gil between alts plus no option to pass bonded or untradable items but it's still better than nothing if you really really want to max desynth on all classes.

I do agree that the cap is stupid. However, I do believe it is probably just there for now, and will probably be patched out of the game at some point, if there's enough demand for it.

I quite doubt that it would be changed - it was clearly stated fairly early that you'd not be able to level up / max out all classes on desynth, originally it even looked like it would be possible on only one so I'd say that (almost) three is quite acceptable compromiss. If you really want / "need" them all see my comment above.